Wired for Rewards

Published: Winter 2011-12

The maxim, “With age comes wisdom,” may in fact have a neurological basis.
That’s what Darrell Worthy, assistant professor of psychology at Texas A&M University, suspects. His experiments show that older adults tend to make decisions based on long-term benefits, while younger subjects are driven more by instant gratification.

Are those differences due at least partly to age-related differences in the brain? Worthy and fellow researchers hope to answer that question by running functional magnetic resonance imaging (fMRI) scans on the brains of people as they make decisions.
A growing number of scientists, including Worthy, believe the ventral striatum section of the brain is involved in instant gratification, while the prefrontal cortex is more connected to delayed gratification. “Aging leads to a lot of decline in different neural areas, and one of those areas is the ventral striatum,” Worthy explains. “That area is implicated in assigning value to the immediate rewards you receive. Anytime you are rewarded or punished the area becomes activated.” He and his colleagues are investigating whether the frontal areas of the brain that are used in more conscious, deliberative processing become more active in older adults to make up for other age-related changes.
Researchers also are studying links between the ventral striatum and prefrontal cortex. “Just looking at those two parts may be too simplified,” Worthy says. “There’s an emerging distinction between the networks linking the striatum to the prefrontal cortex. The limbic loop appears to be related more to emotion and immediate gratification, while the cognitive and motor loops would be related more to delaying gratification.”
Another major study of instant versus delayed gratification also showed the importance of the ventral striatum and prefrontal cortex. University researchers recently did a follow-up study with some of the people who participated in the well-known marshmallow experiment at Stanford University some 40 years ago when they were 4 years old. The study examined the behavior of the subjects — now adults in their 40s — to determine whether they demonstrated the same tendency toward instant or delayed gratification that they did as children when choosing between eating one marshmallow now or waiting a while to get two.
Not only did the study show that the tendency toward instant or delayed gratification remained constant over time, but through the use of fMRIs, it also found differences in the brain activity of the subjects. “The ventral striatum that has been implicated in reward and risk-taking showed a difference between groups, as well as the ventral prefrontal cortex, a region implicated in impulse control,” says BJ Casey, director of the Sackler Institute for Developmental Psychobiology at Weill Cornell. “These regions have been shown to be involved in addiction and substance abuse.”
Such brain research could lead to greater understanding and perhaps even new treatments for various addictions and other problems related to impulse control and instant gratification.